Multimedia information is composed of several objects that constitute a document. These objects could be of different data types, such as text, still images, video, and sound. In order for these objects to be meaningful to a user, there must be a logical and temporal structure of the objects constituting the documents' contents. To ensure this logical and temporal structure, e.g. when displaying a video sequence on a display device and providing a soundtrack for this video sequence via an adapter card to a speaker, the respective data streams have to be synchronized and scheduled before being sent to the output devices. The same principle applies to other related multimedia information which has to be synchronized in communicating with other devices or users (e.g. teleconferencing), before processing and presentation.
Synchronization and scheduling is a critical task for a wide spectrum of applications ranging from computer-integrated telephony, text with voice annotations, any kind of multi media systems, and interactive services (e.g. interactive television) to cooperative teleworking on documents including foils and video, and distributed games. A further application, where information streams have to be synchronized, is known as medical imaging, for which high-resolution images must be distributed reliably and fast throughout a hospital.
To date, the synchronization is typically performed in software. However, if the scheduling intervals are too short, or if too many information streams must be synchronized, a software solution, which is very CPU intensive, is often the limiting factor as far as processing speed is concerned.
In real-time systems time-critical tasks have to be scheduled reliably and fast. In the present context, any system in which the time at which an output is produced is significant, is referred to as real-time system. The lag from the input time of a real-time system to its output time, i.e. the delay, must be sufficiently small for acceptable timeliness. In other words, a real-time system has to respond to an externally-generated input stimuli within a finite and specified period. In hard real-time systems, i.e. in those systems where it is absolutely imperative that responses occur within a specified deadline, scheduling of time-critical tasks is of particular interest. However, the present invention is not limited to hard real-time systems. It might be used in soft real-time systems, too. Such a soft real-time system would still function correctly if deadlines are occasionally missed, and a hardware solution in accordance with the present invention might be to costly under certain circumstances.